The price includes 19% sales tax. Also included is the "mineral oil tax" and an Öko (ecological) tax. I don't know the how much of the retail price is the tax in case of motor oil, but in the case of gasoline it is about 70%.
You can buy heavily discounted oil at home improvement centers in Germany. Those are shops similar to The Home Despot. One big chaain in Germany and other European countries, is OBI Baumarkt. They sell large jugs of oil, including recycled oil.
There's a blast from the past! I see Jet oil. I used to gas up at Jet gas stations all the time. I never used their oil, though.